This invention pertains to well drilling apparatus, more particularly to controls for down hole drilling motors. The preferred embodiment is used as part of the drill string, just above the motor to sense stall speed and to open a by pass channel to shunt drilling fluid around the stalled motor to the well annulus. In one configuration the by-pass channel is through a bore in the rotor of the motor.
Fluid powered drilling motors in common use are of the turbine type or positive displacement type. Turbine types can stall while drilling but the motor is usually not damaged as a result. Drilling motors of the positive displacement type, known as progressing cavity motors, have the ability to stall when overloaded and such stall conditions will, in time, damage the motor. The stalled condition does not stop the movement of fluid through the motor and damage to the elastomer stator often results if allowed to continue for some time. If the stall is sensed at the surface, the flow of drilling fluid can be stopped before damage occurs. One stall indicator is zero penetration of the drill head but that takes too long to recognize. Pressure drop through a stalled motor should increase enough for stall detection but motors are very often operated with torque near the stall condition and the pressure difference is often lost in the much higher pressure in the overall drilling fluid circuit. A positive indication of stall is needed and by-passing of the fluid around the motor to the well bore would give a positive signal in the form of a significant drop in stand pipe pressure at the surface. Further, by-passed drilling fluid would protect the motor to some extent even before the signal brings on corrective actions at the surface. The drill head can be lifted from the well face to allow the motor to restart and drilling can continue.
The apparatus is housed in a length of drill string that is installed in the drill string just above the motor. The drilling motor is a part of the drill string. The housing may be part of the motor body, or it may be a separate drill string element attached to the motor body. Drilling fluid flows through the housing from the drill string bore to the motor. In the housing a rotational control sensor is associated with a valve actuator that will be opened by the apparatus when the rotor of the motor is turning at less than a preselected speed. Several methods for rotor speed sensing are disclosed. Sensed orbital speed is an indirect indication of rotational speed.
One sensor utilizes an oil pump driven by the rotor to produce oil pressure to actuate the by-pass valve and a designed leak in the circuit reduces the oil available to actuate the valve to open the by-pass if the rotor speed is below a preselected amount. That arrangement combines rotor speed sensing and valve actuation.
An alternate arrangement utilizes a pivotable weight that the orbital action of the rotor displaces to actuate a servo valve to control mud flow to actuate the by-pass actuation piston to control the motor by-pass circuit. The mass of the pivotable weight and the strength of a mass centering spring comprise a motor speed sensing means.
By selection of apparatus disclosed, the motor by-pass control valve can direct by-passed drilling fluid through a bore in the rotor or through the housing wall directly to the well annulus. The rotor bore route dumps the by-passed fluid below the motor power generating structure. The rotor bore in motors now operating opens within the motor above the drill head.
To reset the system, to start the motor and close the by-pass, the drill string can be lifted to relieve torque drag on the drill head. The motor will normally restart and motor rotation will close the by-pass and drilling can continue.
Signals, as defined herein, comprise movement of elements or change in conditions, such as fluid flow resistance, initiated to cause a preplanned response action at a remote place. The change in fluid flow resistance at a down hole location, to cause a change in pressure at a surface location, for the purpose of indication that a down hole condition has changed is a signal. This is anticipated by and is within the scope of the claims. That definition of signals is not contrary to the general understanding of the definition used by those skilled in the art involved.
It is an object of this invention to provide apparatus to sense motor rotation and produce an output signal to a valve actuator to open a controlled motor by-pass drilling fluid channel when the motor speed is less than a preselected amount.
It is another object of this invention to close a motor by-pass fluid channel when sensed motor speed exceeds a preselected amount.
It is yet another object of the invention to detect the orbiting of the rotor centerline about the housing centerline to sense the causative rotor rotation.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.